JP2000018247A - Variable capillary device for oil static pressure bearing and movement error correcting method utilizing it - Google Patents

Abstract

PROBLEM TO BE SOLVED: To allow a capillary conpensating element to be variable set in order to impart the rigidity to an oil static pressure bearing. SOLUTION: This device is made in a cylindrical form, and furnished with the upper side and the lower side structures, and a leaf spring inserted in the middle part. Between the center part of the upper side structure and the leaf spring, a minute interval is formed, which plays the role of a capillary. As the correcting method, a pair of oil static pressure bearings where a pair of variable capillary devices 402 and 404 is connected respectively is set at one side, while a pair of oil static pressure bearings where a pair of fixed capillary devices 702 and 704 is connected is set at the other side, and a stage to find the gains of the pair of variable capillary devices 402 and 404; a stage to transfer the table 810, and to measure the error displacement; and the stage to apply the correcting voltage to the movable capillary devices 402 and 404 while the table is transferred; are included. This device and the movement error correcting method make a capillary conpensating element variable set to impart a rigidity to the oil static pressure bearings, and can correct the relative displacement correspondent to the movement error at the positions of a spindle or a transfer table by utilizing the resistance variation of the conpensating element.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a hydrostatic bearing, and more particularly, to various kinds of ultra-precision measuring equipment, ultra-precision measuring equipment and operation of a machine tool by adjusting a pocket pressure of the hydrostatic bearing. BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a capillary device for a hydrostatic bearing capable of correcting a motion error generated therein and a motion error correction method using the same.

[0002]

2. Description of the Related Art Hydrostatic bearings are non-contact type bearings.
A fluid, such as air or lubricating oil, is guided into the interior to restrict the discharge of the fluid, thereby retaining a supporting force. The hydrostatic bearing reduces the low-frequency error component transmitted along the main shaft or the guide rail by the averaging effect of the oil film formed between the facing object and the high-damping characteristic to attenuate the high-frequency vibration. It is adapted to the main spindle and transfer table for precision machine tools, and is mainly used for the main spindle and guide surface for various precision grinding machines and the guide surface of ultra-precision machine tools.

FIG. 1 shows the principle of a hydrostatic bearing 100 and an equivalent electric circuit. The table on which the bearing 100 is installed moves linearly along the guide surface 120. The table maintains a predetermined distance from the guide surface 120 by a high-pressure thin oil film sprayed from a pocket 130 formed on an upper surface of the table. A plurality of pockets may be formed in the transfer table of the machine tool, and the inflow of fluid from the plurality of pockets may apply an appropriate pressure to the guide surface according to a load applied to the table. Is adjusted to In the case of the pad-shaped section, the bearing gap h is, as shown in the mathematical formula 1, the sum of the load W (including the table's own weight) W applied to the table and the pressure formed between the guide surface and the table by hydrostatic pressure lubrication. It is calculated from the principle that P is the same as the value obtained by integrating P with respect to the entire area A of the bearing. That is,

(Equation 1) here

(Equation 2) The ratio by dimensionless area and dimensionless oil amount coefficient of the pocket area to total area bearing, P _S is the supply pressure, P _r of the lubricating fluid supply device is a pocket pressure, k _c is used to provide rigidity to the bearing Means the capillary coefficient of the capillary used.

(Equation 3) The value increases as the ratio of the pocket area increases.

On the other hand, the hydrostatic bearing has an advantage that the friction is small and high precision is maintained by an averaging effect, but it has a disadvantage of low rigidity. In order to increase the rigidity of the hydrostatic bearing, it is efficient to minimize the bearing gap. In addition, in order to optimally design a bearing that satisfies the minimum bearing gap, it is necessary to limit the amount of fluid flowing into the bearing by the bearing gap.

[0005] However, in order to reduce the bearing gap, the machining precision of the bearing must be increased. Therefore, there is a limitation in improving the rigidity of the bearing as a method of reducing the bearing gap. To overcome the limitations, various variable mechanisms have been proposed.

FIGS. 2 and 3 show diaphragm type variable limiting bearings 200 and 250 as an example of such a mechanism. 2 and 3, the bearing surface 2
Reference numerals 10 and 260 denote elastically deformable diaphragms. The state of the bearing surfaces 210 and 260 is the bearing 200 and 2
Bearing surfaces 210 and 26 due to a change in load applied to
It is deformed by a pressure change acting on zero. Thus, high rigidity is achieved. In particular, in the mechanism shown in FIG. 3, the inner peripheral surface of the diaphragm 260 is elastically supported by the O-ring 270. The pressure on the rear surface of the diaphragm 260 is changed by the pressure acting on the bearing surface 260 through a small hole 290 formed in the center of the housing. Thus, the state of the diaphragm changes sensitively with the change in load.

When the above-mentioned diaphragm type variable limiting mechanism is used under appropriate bearing conditions, high bearing rigidity can be obtained. However, the diaphragm type variable limiting mechanism has the following disadvantages. (1)
Its application is limited because the bearing surface has to be deformed. (2) When the diaphragm is largely deformed, a pocket is formed. Accordingly, the diaphragm can vibrate by compression of air.
(3) It is not easy to process the diaphragm.
The life of the diaphragm is affected by changing the bearing characteristics depending on the processing precision.

On the other hand, in order to manufacture a spindle or a table using a hydrostatic bearing, when the spindle is a spindle, machining precision such as the epicenter and cylindricity of the shaft is required, and in the case of a transfer table, at least two guides are used. The straightness, flatness, squareness and relative parallelism of the two rails with respect to the rails,
Since it is necessary to obtain machining precision such as perpendicularity, it is not easy to achieve submicron motion precision even if an oil film averaging effect is expected. Further, since the motion error based on such a machining error depends on the geometrical shape, it is difficult to correct the motion error even if the peripheral device is refined.

Conventionally, three types of correction have been proposed.
First, there is a fixed correction used for a fixed value resistor where the capillary or orifice is fixed. Second, the variable compensation uses a diaphragm and a valve to form a flow that is inversely proportional to the pocket resistance, thereby achieving a pressure difference greater than the pressure difference created by the fixed compensation device. However, all of the two correction schemes described above require that each device be adapted to the bearing gap.

[0010] Smaller bearing gaps are required to improve the performance of the bearing and the compensator requires manual tuning, resulting in manufacturing errors and making the two compensation schemes more difficult to use. In addition, a machine tool having three axes requires almost 36 bearing pockets, so that labor consumption is very large.

A third type of correction is so-called self-correction, which uses changes in the bearing gap to itself permit changes in fluid flow into the pocket. In the self-correction method, a method of forming a linear groove on a bearing surface by a bearing surface is mainly applied to a spindle. But,
Although the self-correction method did not show an excellent effect in terms of economy, it is difficult to quantitatively analyze the flow pattern, and it is particularly difficult to determine the flow near the end of the linear groove. Difficulty results in improper resistor design, which eventually requires manual tuning of the corrector. In addition, the self-correction unit using the linear groove as described above has a disadvantage that it cannot be used in a structure in which the groove cannot be formed properly.

[0012]

SUMMARY OF THE INVENTION Accordingly, the present invention has been made to solve the above problems of the prior art, and a first object of the present invention is to provide a hydrostatic bearing with rigidity. An object of the present invention is to provide a variable capillary device capable of changing a capillary compensation element to be installed. Also, a motion error using a variable capillary device capable of correcting a relative displacement corresponding to a motion error amount at each position of a main shaft or a transfer table using the variable capillary device using a resistance change of a compensation element. It is to provide a correction method.

[0013]

SUMMARY OF THE INVENTION In order to achieve the first object, the present invention provides a base plate, a hollow first cylinder member connected to an upper surface of the base plate, and an upper part of the first cylinder member. A first means for guiding the flow of the fluid, the fluid being provided between the first cylinder member and the first means, the fluid being introduced into the first means by changing its state; And a third means for changing the state of the second means.

According to a preferred embodiment of the present invention, the first means includes a hollow second cylinder member having the same outer diameter as the first cylinder member and having an open bottom surface. A first opening for introducing the fluid into the second cylinder member is formed at an upper portion of the second cylinder member, and an annular guide having an inner diameter substantially equal to the size of the first opening is formed in the second cylinder member. The fluid, which extends downward from the first opening integrally with the first opening and guides the fluid flowing through the first opening to a lower portion of the second cylinder member, flows into one side of the second cylinder member. A second opening for discharging the discharged fluid to the outside is formed.

On the other hand, the first and second openings are internally threaded, and are internally threaded. The first and second pipes are connected to a fluid supply source and the second pipe is connected to a hydrostatic bearing. The fluid supply source and the hydrostatic pressure bearing are connected to each other by being meshed with the portion.

According to a preferred embodiment of the present invention, the second means is a circular leaf spring, the size of which is the same as the outer diameter of the first and second cylinder members; The space between the capillaries formed between the upper surface and the lower end of the annular guide is changed by press-fitting the members and changing the degree of upward bending by the force applied from the bottom surface. Accordingly, the amount of the fluid flowing into the second cylinder member is adjusted.

According to a preferred embodiment of the present invention, the third means is a piezoelectric element installed in the first cylinder member such that an upper end thereof is in contact with a bottom surface of the leaf spring, and the third means is applied to the piezoelectric element. The displacement of the upper end of the piezoelectric element from above is changed by the applied voltage to change the distance between the capillaries.

When the voltage applied to the piezoelectric element is increased, the upper end of the piezoelectric element is moved upward, whereby the distance between the capillaries is reduced, so that the second position is reduced.
When the amount of the fluid flowing into the cylinder member decreases, and conversely, when the voltage applied to the piezoelectric element decreases, the upper end of the piezoelectric element moves downward, thereby increasing the gap between the capillaries. The amount of the fluid flowing into the second cylinder member increases.

According to a preferred embodiment of the present invention, an adjusting screw is provided on a bottom wall of the first cylinder member, and the adjusting screw is adjusted to adjust the overall vertical position of the piezoelectric element, thereby adjusting the position of the capillary. Set the initial interval.

According to the present invention, there is provided a fluid supply source having first and second inlets connected thereto.
The first, second, third and fourth hydrostatic bearings in which the outlets of the variable capillary device, the first and second fixed capillaries and their respective pockets are communicated, are placed in parallel with each other. A method for correcting a motion error of a table in which first and second guide rails are extended and movably connected in a first direction to first and second guide rails, wherein: Installing the first hydrostatic bearing on a first side of a first surface facing the vertical surface of the guide rail; and (2) the first side of the first surface of the table bottom portion and the first direction. The second side is separated from the second side by a predetermined distance.
Installing a hydrostatic pressure bearing; and (3) a second surface of the table bottom surface facing the vertical surface of the second guide rail, which is orthogonal to the first side of the first surface and the first direction. Installing the third hydrostatic bearing on a third side at a position aligned in the second direction, and (4) connecting the second side of the second surface of the table bottom surface to the second side of the first surface. Installing the fourth hydrostatic bearing on a fourth side arranged in the second direction;
(5) applying a stepwise increasing voltage to the first and second variable capillary devices to measure the displacement of the table in the second direction at each stage; and (6) the first and second variable capillary devices. Determining the first and second gains of the first and second variable capillary devices by calculating the relationship between the voltage applied to the two variable capillary devices and the resulting displacement of the table in the second direction; (7) transferring the table in the first direction without applying a voltage to the first and second variable capillary devices, and moving the table and the first and second guides in the second direction of the table; Measuring an error displacement based on the error of the straightness and parallelism of the rail;
(8) The first and second gains obtained from the step (6) are used to cancel the error displacement while the table is moved in the first direction.
And applying a correction voltage that changes according to the changing error displacement to the second variable capillary device.

According to a preferred embodiment of the present invention, in the step (5), the displacement of the table in the second direction includes the first side of the first surface of the table and the second side of the second surface.
A first position aligned in a direction, a first position of the table on the first surface and a first position aligned in a second direction, a table on the first surface on the second side and the second direction. Are measured at a second position and a third position located at the center of the first and second positions, respectively.

In the step (5), the gradually increasing voltage is applied to the first and second piezoelectric elements installed in the first and second variable capillary devices, so that the first and second variable capillary devices have the same structure. And a first and a second for adjusting the amount of fluid discharged to the first and second variable capillary device outlets.
The position of the table in the second direction is changed by changing the pocket pressure of the first and second hydrostatic bearings by adjusting the interval between the capillaries.

On the other hand, in the step (6), the first and second gains are obtained by making the relationship between the voltage and the displacement substantially linear for the first and second variable capillary devices.

In the step (7), the voltage applied to the first and second variable capillary devices when the table is moved in the first direction is specified because the error displacement has repetitiveness. .

According to a preferred embodiment of the present invention, the first and second variable capillary devices each include first and second piezoelectric elements having a maximum displacement amount capable of canceling the error displacement. The error displacement includes a straightness error of the table and the first and second guide rails in the first direction, and a rotation error in a vertical direction orthogonal to the first and second directions. The degree error and the rotation error are simultaneously corrected by making the voltages applied to the first and second variable capillary devices different according to the obtained first and second gains of the first and second variable capillary devices. Is done.

[0026]

The variable capillary device for an hydrostatic pressure bearing according to the present invention and the method of correcting a motion error using the same according to the present invention vary the capillary compensating element installed to provide rigidity to the hydrostatic pressure bearing. The relative displacement corresponding to the amount of motion error at each position of the main shaft or the transfer table can be corrected using the resistance change of the compensation element.

The above objects and other features and advantages of the present invention will become apparent from the following description of some preferred embodiments of the present invention to which reference is now made.

[0028]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A variable capillary device 400 for a hydrostatic bearing 500 according to a preferred embodiment of the present invention and the operation principle of the variable capillary device 400 will be described in more detail with reference to the accompanying drawings. FIGS. 4 and 5 show a variable capillary device 400 for a hydrostatic bearing according to a preferred embodiment of the present invention, and its operating principle. Referring to FIGS. 4 and 5, the variable capillary device 400 includes a circular base plate 41.
0, a hollow first cylinder member 420 coupled to an upper surface of the base plate 410, coupled to an upper portion of the first cylinder member 420, for guiding the flow of fluid supplied at a static pressure from the fluid supply source Ps. According to a preferred embodiment of the present invention, between the first cylinder member 440 and the hollow second cylinder member 440 having the same outer diameter as the first cylinder member 420 and having an open bottom surface. And the state of the second cylinder member 44 is changed.
The upper end of the circular plate spring 430 contacts the bottom surface of the plate spring 430 in the first cylinder member 420 to change the state of the circular plate spring 430 for adjusting the amount of the fluid flowing into the first cylinder member 420. The piezoelectric element 450 is installed as follows.

A first opening 470 for introducing the fluid into the second cylinder member 440 is formed at an upper portion of the second cylinder member 440. In order to guide the fluid flowing through the first opening 470 to the lower portion of the second cylinder member 440, an annular guide 480 having an inner diameter substantially equal to the size of the first opening 470 is integrated with the second cylinder member 440. First
It must extend downward from the opening 470.
According to the preferred embodiment of the present invention, the lower end of the annular guide 480 forms a capillary 432 having a fine distance h with the upper surface of the leaf spring 430. According to a preferred embodiment of the present invention, the fine gap h has a size on the order of tens of microns.

The upper end of the piezoelectric element 450 is displaced upward by the voltage applied to the piezoelectric element 450 installed in the first cylinder member 420, and the distance h between the capillaries 432 is changed.
To change. The size of the leaf spring 430 is the same as the outer diameter of the first and second cylinder members 420 and 440, and
And between the upper surface and the lower end of the annular guide 480 by being inserted between the upper surface and the lower end of the annular guide 480 by being pushed into the space between the upper surface and the second cylinder members 420 and 440. The amount of the fluid flowing into the second cylinder member 440 is adjusted by changing the distance h between the capillaries 432 to be formed.

That is, when the voltage applied to the piezoelectric element 450 is increased, the upper end of the piezoelectric element 450 is moved upward, whereby the distance h between the capillaries 432 is reduced, so that the capillary 432 flows into the second cylinder member 440. When the amount of the fluid decreases and, conversely, the voltage applied to the piezoelectric element 450 decreases, the upper end of the piezoelectric element 450 moves downward, thereby increasing the interval between the capillaries 432, thereby causing the capillary 432 to move into the second cylinder member 440. The amount of the fluid flowing in increases.

On the other hand, according to a preferred embodiment of the present invention,
An adjusting screw 460 is installed on the bottom wall of the first cylinder member 420. By adjusting the adjustment screw 460 to adjust the overall vertical position of the piezoelectric element 450, the capillary 432 can be adjusted.
The initial interval hi is set.

One side of the second cylinder member 440 has a second opening 49 for discharging the inflowing fluid to the outside.
0 is formed. On the other hand, the first and second openings 470, 4
Reference numeral 90 denotes a first pipe 472 and an hydrostatic bearing 5 whose inner peripheral surfaces are internally threaded and connected to the fluid supply source Ps, respectively.
The fluid supply source Ps and the hydrostatic pressure bearing 500 are engaged with the external thread portion of the second pipe 492 connected to
Is communicated with.

On the other hand, FIG. 5 shows an example of the principle of correcting the movement error of the transfer table using the variable capillary device 400. Referring to FIG. 5, a variable capillary device 400 is attached to an upper pad 510 of an hydrostatic pressure bearing 500 by a lower pad 52.
0 is connected to a general fixed capillary 700. In this state, when it is necessary to displace the hydrostatic bearing 500 by Δh, when a predetermined voltage is applied to the piezoelectric element 450, the capillary 4
32, the spacing h is reduced, which increases the resistance and instantaneously reduces the pocket pressure in the upper pad 510. At this time, the upper and lower pads 510 and 520 are
Since the forces formed by the integration of the pressure distribution applied to zero must be the same, the upper pad 510 is displaced downward by Δh so that the pocket pressure of the upper pad 510 is increased. If the applied voltage to be applied to the piezoelectric element 450 and the amount of displacement of a table (not shown) are determined in advance using such a principle, the piezoelectric element 45
The motion error of the table occurring within the maximum displacement amount of 0 can be corrected.

FIG. 6A shows a response to a 1 V / step input of a D / A converter 800 (shown in FIG. 7) on the table surface on the pad 510 side to which the variable capillary device 400 is connected at a supply pressure of 100 N / cm ³ . The response displacement of the table appropriately follows the input value, and the response gain (gain) for the D / A converter is 0.5.
It shows that it is 5 μm / V. FIG. 6B shows the response displacement measured on the opposite pad 520 to which the fixed capillary 700 is connected, and shows the same amount of displacement as in FIG. 6A. Can be confirmed that there is almost no. FIG. 6C and FIG.
(D) shows the change in the pocket pressure of both pads 510 and 520 at that time.
Can be confirmed that the pocket pressure is well followed. Thereby, it can be confirmed that the table has moved to the new parallel position of the both-side pocket pressure.

Hereinafter, a method of correcting a motion error of a hydrostatic table using a variable capillary device 400 according to a preferred embodiment of the present invention will be described in detail with reference to the accompanying drawings. FIGS. 7 and 8 show the structures of an experimental device 900 and an experimental hydraulic static pressure table 810 for correcting a motion error of the hydraulic static pressure table 810. FIG. Referring to FIGS. 7 and 8, the hydrostatic pressure table 8
Numeral 10 denotes a double-sided pad system, in which first and second capillary devices 402 and 40 each having an inlet connected to a fluid supply source Ps.
4. First, second, and third ports in which respective outlets of the first and second fixed capillaries 702 and 704 communicate with their respective pockets.
And a fourth hydraulic static pressure bearing are installed so that the first and second guide rails 910 and 912 and the first and second guide rails 910 and 912 which are parallel to each other are movable in a first direction X which is extended. Be combined.

Referring to FIG. 10, the hydrostatic pressure table 81
0 is set as follows. (1) A first surface of the bottom surface of the table 810 facing the vertical surface of the first guide rail 910.
The first hydrostatic bearing 840 is installed on the first side 812a of the surface 812 (step S1). (2) A second hydrostatic bearing 8 is provided on a second side 812b of the bottom surface of the table 810, which is separated from the first side 812a of the first surface 812 by a predetermined distance in the first direction X.
42 is installed (step S2). (3) Table 81
The third surface 814 of the second surface 814 facing the vertical surface of the second guide rail 912 on the bottom surface of the first surface 812 is aligned with the first side 812a of the first surface 812 in the second direction Y orthogonal to the first direction X. Side 8
The third hydrostatic bearing 850 is installed at 14a (step S3). (4) Second surface 814 on the bottom surface of table 810
A fourth hydrostatic bearing (not shown) is installed on the fourth side 814b of the first surface 812 aligned with the second side 812b of the first surface 812 in the second direction Y (step S4).

The table 810 has a ball screw 920
And an AC servomotor 998 and a DSP motion controller 996. In order to apply linear displacement and angular displacement to the table 810 using the two variable capillary devices 402 and 404, the gain value of the first and second variable capillary devices 402 and 404, that is, table displacement / D /
It is necessary to experimentally obtain the A converter input voltage in advance. For this, (5) the first and second variable capillary devices 4
A voltage that gradually increases in steps 02 and 404 is applied to measure the displacement of the table 810 in the second direction Y at each step (step S5). (6) By calculating the relationship between the voltage applied to the first and second variable capillary devices 402 and 404 and the resulting displacement of the table 810 in the second direction Y, the first and second variable capillary devices 402 and 404 are calculated. First of 404
And a second gain (step S6).

At this time, according to a preferred embodiment of the present invention, as shown in FIG. 7, in step S5, the displacement of the table 810 in the second direction Y is equal to the first side 812a of the first surface 812 of the table 810, as shown in FIG. A first position aligned in the two directions Y, a second position aligned in the second direction Y with the second side 812b of the first surface 812 of the table 810, and a third position positioned in the center of the first and second positions, respectively. Measured.

First and second variable capillary devices 402 and 40
And the first and second piezoelectric elements 402a, 40
4a for controlling the amount of fluid formed in the first and second variable capillary devices 402 and 404 and discharged to the first and second variable capillary device outlets 402b and 404b by applying the gradually increasing voltage to 4a. First and second capillaries 402c, 4
By adjusting the interval of 04c, the respective pocket pressures of the first and second hydrostatic bearings are changed to change the position of the table 810 in the second direction Y. The relationship between the voltage and the displacement for each of the first and second variable capillary devices 402 and 404 is obtained by substantially linearizing the relationship.

At this time, the horizontal displacement of the table 810 is measured using the capacitive sensor 988. Thereafter, the correction method includes the steps described below. (7) The table 810 is moved in the first direction X without applying a voltage to the first and second variable capillary devices 402 and 404, and the table 810 and the first and second guides are moved in the second direction Y of the table 810. The error displacement based on the errors of the straightness and parallelism of the rails 910 and 912 is measured (step S7).
(8) While the table 810 is moved in the first direction X, the first and second variable values can be offset by the first and second gains obtained from the step (6) so as to cancel the error displacement. A correction voltage that changes in accordance with the changing error displacement is applied to the capillary devices 402 and 404 (step S8).

In step S7, the error displacement has a repeatability, so that the first direction X
At the time of transfer to the first and second variable capillary devices 402 and 40
The voltage applied to 4 is specified.

According to a preferred embodiment of the present invention, the first and second variable capillary devices 402 and 404 respectively include first and second piezoelectric elements 402a and 404a having a maximum displacement amount capable of canceling the error displacement. Can be provided.

The error displacement is calculated by moving the table 8 in the first direction X.
10 and a straightness error of the first and second guide rails 910 and 912 and a rotation error in a vertical direction orthogonal to the first and second directions X and Y, and the straightness and the rotation error are obtained by the above-mentioned calculation. First and second variable capillary devices 4
The first and second gains 02 and 404 make the voltages applied to the first and second variable capillary devices 402 and 404 different from each other, so that they are corrected simultaneously.

FIG. 9A shows the horizontal linear motion error and the angular motion error of the hydrostatic pressure table 810, each of which is repeatedly measured five times. It shows a linearity of 2.21 μm and a degree of angular movement of 1.4 arcsec for a movement distance of 200 mm. On the other hand, FIG. 9B shows the degree of movement when the variable capillary device is used. As a result of simultaneously correcting the linear motion error and the angular motion error by applying the motion error correction method using the variable capillary device, the linear motion error is approximately 1/10 of the uncorrected state, 0.25 μm.
Thus, it can be confirmed that the angular motion error is improved at 0.4 arcsec, which is approximately 1/3 of the uncorrected state, and is very effective in correcting the error of the hydrostatic pressure table 810.

[0046]

As described above, the variable capillary device for an hydrostatic bearing according to the present invention and the method of correcting a motion error using the same include a capillary compensating element installed for providing rigidity to the hydrostatic bearing. It is possible to correct the relative displacement corresponding to the amount of motion error at each position of the spindle or the transfer table by using the resistance change of the compensation element.

Although the present invention has been described in detail with reference to embodiments, the present invention is not limited to the embodiments, and any person having ordinary knowledge in the technical field to which the present invention belongs may depart from the spirit and spirit of the present invention. Rather, the invention could be modified or changed.

[Brief description of the drawings]

FIG. 1 is a schematic diagram showing an operation principle and an equivalent electric circuit of a general pad-shaped hydrostatic bearing device having a cross section.

FIG. 2 is a sectional view showing a diaphragm type hydrostatic bearing device according to the related art.

FIG. 3 is a cross-sectional view showing a diaphragm type hydrostatic bearing device according to the related art.

FIG. 4 is a perspective view of a variable capillary device according to a preferred embodiment of the present invention;

FIG. 5 is a schematic diagram illustrating a principle of correcting a motion error of a hydrostatic table using a variable capillary device according to a preferred embodiment of the present invention.

FIG. 6A is a graph showing a displacement and a pocket pressure when a step voltage is input to a variable capillary device according to a preferred embodiment of the present invention. 4B is a graph showing a displacement and a pocket pressure when a step voltage is input to the variable capillary device according to a preferred embodiment of the present invention. c is a graph showing the displacement and pocket pressure when a step voltage is input to the variable capillary device according to a preferred embodiment of the present invention. 4D is a graph showing a displacement and a pocket pressure when a step voltage is input to the variable capillary device according to a preferred embodiment of the present invention.

FIG. 7 is a schematic diagram showing an experimental apparatus for simultaneously correcting the linearity and angular motion error of a hydrostatic table using a variable capillary device according to a preferred embodiment of the present invention.

FIG. 8 is a sectional view showing the structure of the hydrostatic table shown in FIG. 7;

9A is a graph showing a correction result of a linearity and an angular motion error of the hydrostatic pressure table using the experimental apparatus shown in FIG. 7; 8B is a graph showing correction results of the linearity and angular motion error of the hydrostatic table using the experimental apparatus shown in FIG.

FIG. 10 is a flowchart illustrating a method for simultaneously correcting a linearity and an angular motion error of a hydrostatic table using a variable capillary device according to a preferred embodiment of the present invention.

[Explanation of symbols]

 402, 404: first and second variable capillary devices 402a, 404a: first and second piezoelectric elements 402c, 404c: first and second capillaries 810: hydraulic static pressure tables 702, 704: first and second fixed capillaries h: Bearing gap Pr: Pocket pressure

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[Procedure amendment]

[Submission date] October 5, 1999 (1999.10.
5)

[Procedure amendment 1]

[Document name to be amended] Statement

[Correction target item name] Claims

[Correction method] Change

[Correction contents]

[Claims]

[Procedure amendment 2]

[Document name to be amended] Statement

[Correction target item name] 0008

[Correction method] Change

[Correction contents]

On the other hand, in order to manufacture a spindle or a table using a hydrostatic bearing, when the spindle is a spindle, machining precision such as the epicenter and cylindricity of the shaft is required, and in the case of a transfer table, at least two guides are used. Each straight against the rail
Degree , flatness, squareness and relative parallelism of the two rails,
Since it is necessary to obtain machining precision such as perpendicularity, it is not easy to achieve submicron motion precision even if an oil film averaging effect is expected. Further, since the motion error based on such a machining error depends on the geometrical shape, it is difficult to correct the motion error even if the peripheral device is refined.

[Procedure amendment 3]

[Document name to be amended] Statement

[Correction target item name] 0020

[Correction method] Change

[Correction contents]

According to the present invention, there is provided a fluid supply source having first and second inlets connected thereto.
The first, second, third and fourth hydrostatic bearings in which the outlets of the variable capillary device, the first and second fixed capillaries and their respective pockets are communicated, are placed in parallel with each other. A method for correcting a motion error of a table in which first and second guide rails are extended and movably connected in a first direction to first and second guide rails, wherein: Installing the first hydrostatic bearing on a first side of a first surface facing the vertical surface of the guide rail; and (2) the first side of the first surface of the table bottom portion and the first direction. The second side is separated from the second side by a predetermined distance.
Installing a hydrostatic pressure bearing; and (3) a second surface of the table bottom surface facing the vertical surface of the second guide rail, which is orthogonal to the first side of the first surface and the first direction. Installing the third hydrostatic bearing on a third side at a position aligned in the second direction, and (4) connecting the second side of the second surface of the table bottom surface to the second side of the first surface. Installing the fourth hydrostatic bearing on a fourth side arranged in the second direction;
(5) applying a stepwise increasing voltage to the first and second variable capillary devices to measure the displacement of the table in the second direction at each stage; and (6) the first and second variable capillary devices. Determining the first and second gains of the first and second variable capillary devices by calculating the relationship between the voltage applied to the two variable capillary devices and the resulting displacement of the table in the second direction; (7) transferring the table in the first direction without applying a voltage to the first and second variable capillary devices, and moving the table and the first and second guides in the second direction of the table; Measuring an error displacement based on errors in straightness and parallelism of the rail;
(8) The first and second gains obtained from the step (6) are used to cancel the error displacement while the table is moved in the first direction.
And applying a correction voltage that changes according to the changing error displacement to the second variable capillary device.

[Procedure amendment 4]

[Document name to be amended] Statement

[Correction target item name] 0025

[Correction method] Change

[Correction contents]

According to a preferred embodiment of the present invention, the first and second variable capillary devices each include first and second piezoelectric elements having a maximum displacement amount capable of canceling the error displacement. The error displacement is the true position of the table and the first and second guide rails in the first direction.
A straightness error and a rotation error in a vertical direction orthogonal to the first and second directions, wherein the straightness error and the rotation error are determined by the first and second variable capillary devices. The voltages are applied to the first and second variable capillary devices differently according to the first and second gains, so that they are simultaneously corrected.

Continued on the front page F term (reference) 3C048 BB12 CC07 DD01 3J011 KA07 MA24 3J102 AA02 BA14 CA11 CA31 EA03 EA07 EA10 EA30 EB03 GA01

Claims (10)

[Claims] A first cylinder member coupled to an upper surface of the base plate; a first means coupled to an upper portion of the first cylinder member for guiding fluid flow; A second means installed between the first cylinder member and the first means for adjusting the amount of the fluid flowing into the first means by changing its state;
And a third means for changing the state of the second means. 2. The first means includes a hollow second cylinder member having the same outer diameter as the first cylinder member and having an open bottom surface, and an upper portion of the second cylinder member. Has a first opening for introducing the fluid therein, and an annular guide having an inner diameter substantially equal to the size of the first opening is formed integrally with the second cylinder member. The fluid that extends downward from the opening and flows in through the first opening is guided to a lower portion of the second cylinder member, and the fluid that flows in is discharged to one side of the second cylinder member. The first and second openings are internally threaded, and the first and second openings are connected to a first pipe and a hydrostatic bearing which are respectively connected to a fluid supply source. To be engaged with the external thread of two pipes Variable capillary device of claim 1, further wherein in fluid supply source and communicating with said oil hydrostatic bearings, it is characterized. 3. The second means is a circular leaf spring having the same size as the outer diameter of the first and second cylinder members, and is press-fitted between the first and second cylinder members. By changing the degree of the upward bending by the force applied from the bottom surface, the distance between the capillary formed between the upper edge thereof and the lower end portion of the annular guide is changed, so that the second space is formed. The variable capillary device according to claim 2, wherein an amount of the fluid flowing into the cylinder member is adjusted. 4. The piezoelectric device according to claim 1, wherein the third means is a piezoelectric element installed in the first cylinder member such that an upper end thereof is in contact with a bottom surface of the leaf spring. When the upper end is displaced from above to change the gap between the capillaries and the voltage applied to the piezoelectric element is increased, the upper end of the piezoelectric element is moved upward, whereby the gap between the capillaries is reduced. As a result, the amount of the fluid flowing into the second cylinder member decreases, and conversely, when the voltage applied to the piezoelectric element decreases, the upper end of the piezoelectric element moves downward,
4. The variable capillary device according to claim 3, wherein an amount of the fluid flowing into the second cylinder member is increased by increasing a distance between the capillaries. 5. 5. An adjusting screw is provided on a bottom wall of the first cylinder member to adjust an overall vertical position of the piezoelectric element to set an initial gap between the capillaries. The variable capillary device according to claim 4, wherein: 6. A first and a second variable capillary device each having an inlet connected to a fluid supply source, and a first, a second, and a second, each having an outlet of the first and second fixed capillaries communicating with a respective pocket thereof. Utilizing third and fourth hydrostatic bearings, the first and second guide rails are movably coupled to the first and second guide rails extending in parallel in the first direction. (1) installing the first hydrostatic bearing on a first side of a first surface of the bottom surface of the table facing a vertical surface of the first guide rail; (2) installing the second hydrostatic bearing on a second side of the first surface of the table bottom that is separated from the first side by a predetermined distance in the first direction; and (3) the table bottom. Front of a second surface of the portion facing the vertical surface of the second guide rail Installing the third hydrostatic bearing on a third side of the first surface that is aligned with the first side and a second direction orthogonal to the first direction; and (4) the bottom surface of the table. The fourth side of the second surface is aligned with the second side of the first surface and a fourth side aligned in the second direction.
Installing a hydrostatic bearing; and (5) applying a stepwise increasing voltage to the first and second variable capillary devices and measuring the displacement of the table in the second direction at each step. (6) calculating the relationship between the voltages applied to the first and second variable capillary devices and the resulting displacement of the table in the second direction, by calculating the relationship between the first and second variable capillary devices; And (7) transferring the table in the first direction without applying a voltage to the first and second variable capillary devices, and moving the table in the second direction. Measuring the error displacement based on the errors of the straightness and parallelism of the table and the first and second guide rails; and (8) the error displacement while the table is moved in the first direction. Can offset As described above, the first and second gains obtained from the step (6) are used for the first
Applying a correction voltage that changes in response to the changing error displacement to the second variable capillary device. 7. In the step (5), the displacement of the table in the second direction is a first position aligned with the first side of the first surface of the table in the second direction; A second side aligned with the second side of the first surface in the second direction;
And a third position located at the center of the first and second positions.
The voltage is measured at a position, and the voltage is gradually increased to first and second piezoelectric elements installed in the first and second variable capillary devices, and is formed in the first and second variable capillary devices. Each pocket pressure of the first and second hydrostatic bearings is adjusted by adjusting the distance between the first and second capillaries for adjusting the amount of the fluid discharged to the outlets of the first and second variable capillary devices. 7. The method according to claim 6, wherein the position of the table in the second direction is changed by changing the position of the table. 8. In the step (6), the first and the second
7. The motion error correction using the variable capillary device according to claim 6, wherein the gain is obtained by substantially linearizing the relationship between the voltage and the displacement for the first and second variable capillary devices. Method. 9. In step (7), the voltage applied to the first and second variable capillary devices when the table is moved in the first direction is specified by the repetition of the error displacement. 7. The variable according to claim 6, wherein the first and second variable capillary devices each include first and second piezoelectric elements having a maximum displacement amount capable of canceling the error displacement. A motion error correction method using a capillary device. 10. In step (8), the error displacement is a linearity error of the table and the first and second guide rails in the first direction, and a vertical error perpendicular to the first and second directions. The linearity error and the rotation error are applied to the first and second variable capillary devices according to the determined first and second gains of the first and second variable capillary devices. 7. The method according to claim 6, wherein the correction is performed simultaneously by changing the applied voltages.